Nude swimmers in Thames..!

On the way to the gym around 9am this morning, I was confronted by the sight of two people, male and female, (not teenagers by a long shot..!) disrobing underneath millennium bridge on the southbank of the river and striding joyously into the Thames completely naked. I'm torn as to whether I have complete admiration for such a brave and maverick act on this fine Sunday morning (they didn't seem drunk or in anyway deranged..!), or whether I should have called our local constabulary given that I believe it is technically illegal to swim in this part of the river. Assuming no-one was harmed, I have decided on the former. Anyone else seen such a brave display..?! Needless to say - no pictures were taken as I myself did not want to be arrested.......